Bolted flanges are by far the most widely used and cost effective method of connecting sub-sea pipelines in the oil and gas industry today. The widespread use of this method is largely due to the long-term performance and reliability of sub-sea flanges during the lifetime of the pipeline. Additionally, the level of confidence that pipeline operators have in the integrity of such a connection adds to its universal acceptance as the most appropriate method for connecting pipelines.
Since the inception of this method of connection, the installation of bolted flanges in sub-sea environments has been performed manually by divers. In use, the application of this method is restricted because of the limited depth in which the diver can safely operate. Accordingly, the use of this important connection method has to date been precluded from deepwater applications which extend beyond those depths where it is safe for divers to operate. Rather more elaborate (and expensive) joint types have been developed for diver-less applications. These lack the widespread acceptance of the simple bolted flange.
Technology to enable the installation and use of sub-sea bolted flange connections without divers has therefore been pursued for deepwater applications. This has been done with the aim of using rigid flanged spools, which are the preferred tie-in method for shallower waters, in deepwater applications beyond diver depths. Known systems were designed to make up standard ANSI and API flange joints, for various pipeline tie-in situations, such as spool piece connections and flowline-tree connections. This provided the opportunity of utilising proven technology from shallow water into deepwater applications.
Prior systems for remote bolted flange connection are described in A PIPELINE TIE-IN SYSTEM FOR THE DIVERLESS CONNECTION OF BOLTED FLANGES by Alan West, David Gibson and Ian Frazer, OFFSHORE SOUTH EAST ASIA 1998 and in U.S. Pat. No. 6,234,717 (Corbetta). The paper by West et al describes a system marketed as MATIS by the present applicant, from which the novel system described herein has been developed (MATIS is a registered trade mark). These known systems generally require the deployment of several separate modules for aligning the pipework, and/or for different stages of operation, such as flange alignment, gasket insertion and so forth. The cost of deploying such systems is therefore still quite great, especially as depths increase.
The known remote bolted flange connection system mentioned above generally supplies the flange bolting consumables, such as nuts and bolts (studs), pre-arranged in a manner to suit the pitch circle diameter of the particular flange configuration ready for insertion into the flanges. With the consumables set out in this flange pattern, complications arise when there is a fault with any of the nuts or bolts as the tooling cannot replace failed individual bolts or nuts in order to complete the connection. This problem would not only seriously delay the completion of the connection but would add great expense to the process. Damage to a gasket likewise may render the joint useless.
To solve the problems encountered by the prior art, the question to be resolved is how to achieve completion of the flange connection remotely in deepwater environments when one or more of the consumables have failed or need rectified.
Submersible vehicles can be used for this type of operation but they have the disadvantage of being extremely costly to maintain in operation and the skilled manpower needed to operate them. Additionally, these vehicles are somewhat cumbersome for such an intricate and precise operation and their ability to access certain areas is limited due to their size and shape.